This invention generally relates to printer apparatus and methods and more particularly relates to a thermal ink jet printer for printing an image on a receiver and method of assembling the printer, the printer being adapted for high speed printing and increased thermal resistor lifetime.
An ink jet printer produces images on a receiver medium by ejecting ink droplets onto the receiver medium in an image-wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the ability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
In the case of ink jet printers, at every orifice a pressurization actuator is used to produce the ink droplet. In this regard, either one of two types of actuators may be used. These two types of actuators are heat actuators and piezoelectric actuators. With respect to piezoelectric actuators, a piezoelectric material is used. The piezoelectric material possesses piezoelectric properties such that an electric field is produced when a mechanical stress is applied. The converse also holds true; that is, an applied electric field will produce a mechanical stress in the material. Some naturally occurring materials possessing this characteristic are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, lead metaniobate, lead titanate, and barium titanate. With respect to heat actuators, a heater placed at a convenient location heats the ink and a quantity of the ink phase changes into a gaseous steam bubble. The steam bubble raises the internal ink pressure sufficiently for an ink droplet to be expelled towards the recording medium.
In the case of heat-actuated and piezoelectric actuated ink jet printers, a pressure wave is established in the ink contained in the print head. That is, in the case of piezoelectric actuated print heads, the previously mentioned mechanical stress causes the piezoelectric material to bend, thereby generating the pressure wave. In the case of heat-actuated print heads, the previously mentioned vapor bubble generates the pressure wave. As intended, this pressure wave squeezes a portion of the ink in the form of the ink droplet out the print head. Of course, if the time between actuations of the print head is sufficiently long, the pressure wave dies-out before each successive actuation of the print head. It is desirable to allow each pressure wave to die-out between successive actuations of the print head. That is, actuation of the print head before the previous pressure wave dies-out interferes with precise ejection of ink droplets from the print head, which leads to ink droplet placement errors and drop size variations. Such ink droplet placement errors and drop size variations in turn produce image artifacts such as banding, reduced image sharpness, extraneous ink spots, ink coalescence and color bleeding.
Therefore, in the case of piezoelectric and thermal ink jet printers, printer speed is selected such that the print head is activated only at intervals after each successive pressure wave dies-out. Such delayed printer operation is required in order to avoid interference of a newly formed pressure wave with a preexisting pressure wave in the print head. Otherwise allowing the preexisting pressure wave to interfere with the newly formed pressure wave results in the aforementioned ink droplet placement errors and drop size variations. However, operating the printer in this manner reduces printing speed because ejection of an individual ink droplet must wait for the preexisting pressure wave, caused by ejection of a previous ink droplet, to naturally die-out. Therefore, a problem in the art, for both heat-actuated printers and piezoelectric printers, is decreased printer speed occasioned by the time required to allow a preexisting pressure wave in the print head to naturally die-out before introducing a new pressure wave to eject another ink droplet.
Moreover, in the case of heat-actuated ink jet printers, a heating element, commonly referred to in the art as a xe2x80x9cresistorxe2x80x9d, is in direct contact with the ink in the print head to heat the ink. As previously mentioned, in the case of heat-actuated ink jet printers, a quantity of the ink phase changes into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled to the recording medium. However, it has been observed that over time the ink droplet will xe2x80x9cdecelxe2x80x9d or decelerate and experience a transient decrease in velocity and/or droplet volume after a relatively small number of print head firing cycles. At resumption of firing after a pause, droplet velocity and/or droplet volume recovers, only to decel again in the same manner. Although this phenomenon is not fully understood, the result of xe2x80x9cdecelxe2x80x9d is interference with proper image formation. It has also been observed, in the case of heat-actuated ink jet printers, that resistor performance is decreased by a phenomenon referred to in the art as xe2x80x9ckogationxe2x80x9d. The terminology xe2x80x9ckogationxe2x80x9d refers to the permanent build-up of an ink component""s burned residue on the resistor. This residue limits the resistor""s energy transfer efficiency to the ink and causes the print head to permanently eject droplets with lower velocity or lower droplet volume. Therefore, quite apart from the problem of reduced printer speed, other problems in the art of ink jet printing are decel and kogation.
Also, in the case of heat-actuated ink jet printers, bubble collapse can lead to erosion and cavitation damage to the resistor. In other words, the repeated, relatively high speed collapse of the vapor bubble produces successive acoustic waves that impact the resistor. Over time, these successive impacts combined with the exposure of the resistor to chemical composition of the ink components corrode the resistor. Such cavitation leads to reduced operational life-time for the resistor. Therefore, another problem in the art is cavitation damage to the resistor.
In addition, in the case of heat-actuated ink jet printers, inks must function within a thermal or vaporization constraint. That is, the ink must vaporize at a predetermined temperature in order to form the vapor bubble when required. But for the vaporization constraint required by heat-actuated ink jet printers, various ink components could be included in the ink formulation to enhance printing characteristics. In other words, less soluble components, such as pigments, polymers, or certain surfactants, could be included at higher concentrations in the ink. In general, less soluble components in the ink provide better ink durability on paper because once the ink is deposited on paper, the ink is not easily resolubilized. Also, increasing viscosity or surface tension may improve ink/media interactions that affect print quality (e.g., dot gain, bleed, xe2x80x9cfeatheringxe2x80x9d, or the like), drytime and durability. Therefore, yet another problem in the art are limitations on types of ink useable in heat-actuated ink jet printers, which limitations are caused by constraints placed on vaporization limits of the ink.
Techniques to address the above recited problems are known. For example, an ink jet printer with a flexible membrane between ink and a working fluid is disclosed in U.S. Pat. No. 4,480,259 titled xe2x80x9cInk Jet Printer With Bubble Driven Flexible Membranexe2x80x9d issued Oct. 30, 1984, in the name of William P. Kruger, et al. and assigned to the assignee of the present invention. The Kruger, et al. patent discloses an ink-containing channel having an orifice for ejecting ink and an adjacent channel containing another liquid that is to be locally vaporized. Between the two channels is a flexible membrane for transmitting a pressure wave from a vapor bubble in the adjacent channel to the ink-containing channel, thereby causing ejection of a drop or droplets of ink from the orifice. According to the Kruger. et al. patent, a major advantage of the Kruger, et al. device is separation of the fluid to be vaporized from the ink. In this manner, according to the Kruger et al. patent, this separation permits use of conventional ink formulations, while at the same time making it possible to use special formulations of non-reactive and/or high molecular weight fluid in the bubble-forming chamber in order to prolong resistor lifetime. Moreover, as briefly indicated in the Kruger et al. patent, use of the membrane separating the ink and working fluid is intended to avoid erosion damage to the resistor. However, the Kruger, et al. patent does not address the problem of decreased printer speed occasioned by the time required to allow a preexisting pressure wave in the print head to naturally die-out before introducing a new pressure wave to eject an ink droplet.
A technique for damping a pressure wave to achieve increased printer speed and to prevent satellite ink droplet formation in a piezoelectric ink jet print head is disclosed in U.S. Pat. No. 6,186,610 titled xe2x80x9cImaging Apparatus Capable Of Suppressing Inadvertent Ejection Of A Satellite Ink Droplet Therefrom And Method Of Assembling Samexe2x80x9d issued Feb. 13, 2001, in the name of Thomas E. Kocher, et al. An object of the Kocher, et al. patent is to provide an imaging apparatus capable of suppressing inadvertent ejection of a satellite ink droplet while maintaining printing speed. According to the Kocher, et al. patent, a print head defines a chamber having an ink body therein. A transducer (i.e., a piezoelectric transducer) is in fluid communication with the ink body for inducing a first pressure wave in the ink body. The first pressure wave squeezes an ink droplet from the ink body for ejection of the ink droplet from the print head. However, the first pressure wave is reflected from the walls of the ink chamber. Thus, the first pressure wave forms an undesirable reflected portion of the first pressure wave. This reflected portion of the first pressure wave may have amplitudes sufficient to inadvertently eject so-called xe2x80x9csatellitexe2x80x9d droplets following ejection of the intended ink droplet. Moreover, proper ejection of another ink droplet must await for the reflected portion to naturally die-out. Therefore, the Kocher, et al. device includes a thin piezoelectric sensor wafer spanning the ink channel for sensing the reflected portion of the first pressure wave. Once the sensor wafer senses the reflected portion, a second pressure wave is caused to be generated in the ink channel. According to the Kocher, et al. patent, the second pressure wave has an amplitude and a phase that damps the reflected portion, so that satellite droplets are not formed and so that printing speed is not reduced. However, the Kocher, et al. patent does not address pressure wave damping in a heat-actuated (i.e., non-piezoelectric) ink jet printer. In addition, the Kocher, et al. patent does not address separation of a working fluid from the ink to be ejected.
Therefore, what is needed is a thermal ink jet printer for printing an image on a receiver and method of assembling the printer, the printer being adapted for high speed printing and increased thermal resistor lifetime.
The present invention resides in a thermal ink jet printer for printing an image on a receiver, comprising a print head defining a first chamber therein for receiving a working fluid and defining a second chamber therein; a flexible membrane separating the first chamber and the second chamber; a first transducer in communication with working fluid in the chamber for inducing a first pressure wave in the working fluid in the first chamber, so that said membrane flexes into the second chamber; and a second transducer in communication with the working fluid in the first chamber for inducing a second pressure wave in the working fluid in the first chamber, so that said membrane flexes into the second chamber.
According to an aspect of the present invention, the printer comprises a print head defining a first chamber and a second chamber therein. The first chamber contains a working fluid, such as water. The second chamber contains an ink body in communication with an ink ejection nozzle formed in the print head. A flexible membrane separates the first chamber and the second chamber. A first transducer is disposed in the first chamber and is in communication with the working fluid for inducing a first pressure wave that flexes the membrane into the second chamber. When the first membrane flexes into the second chamber, the first membrane transmits the first pressure wave into the ink body contained in the second chamber. When the first membrane transmits the first pressure wave into the ink body, an ink droplet is ejected out the ink ejection nozzle. A second transducer is disposed in the first chamber and is also in communication with the working fluid for inducing a second pressure wave that flexes the membrane into the second chamber. When the membrane flexes into the second chamber, the membrane transmits the second pressure wave into the ink body contained in the second chamber in order to damp the first pressure wave that was transmitted into the second chamber. The second pressure wave is sufficient to interfere with and damp the first pressure wave but insufficient to cause ejection of another ink droplet. The tranducers themselves may be thermal resistors, electromagnets, piezoelectric actuators, or similar devices for transforming energy input of one form (i.e., heat or electricity) into energy output of another form (i.e., hydraulic or mechanical movement).
A feature of the present invention is the provision of a first transducer separated from the ink body by a membrane, the first transducer generating a first pressure wave to flex the membrane and thereby transmit the first pressure wave to the ink body in order to eject an ink drop from the ink body.
Another feature of the present invention is the provision of a second transducer separated from the ink body by the membrane and spaced-apart from the first transducer, the second transducer generating a second pressure wave to flex the membrane and thereby transmit the second pressure wave to the ink body in order to damp the first pressure wave in the ink body.
An advantage of the present invention is that printer speed is increased.
Another advantage of the present invention is that the effect of xe2x80x9cdecelxe2x80x9d is reduced.
An additional advantage of the present invention is that use thereof reduces the phenomenon known as resistor xe2x80x9ckogationxe2x80x9d.
Yet another advantage of the present invention is that resistor cavitation damage due to the combined effects of bubble collapse and corrosive inks are reduced.
Still another advantage of the present invention is that a wider variety of inks may be used for printing.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there are shown and described illustrative embodiments of the invention.